The present invention relates to the handling of thick, viscous or thixotropic materials, and in particular to the reclamation from storage lagoons of dry, semidry or nearly gelatinous sludge produced as a by-product of various manufacturing operations and/or various conventional waste sludge sewage treatment processes. Most particularly, however, the invention relates to a cake sensor which determines the quality of the dewatered sludge removed from the lagoons by using as the criteria the desirability and suitability of the dewatered sludge for use as land fill material.
Although the actual chemical composition of the materials to be removed from catch basins or lagoons will vary from location to location, normally such materials have been deposited in a liquid or semiliquid state and have been stored in such lagoons or catch basins for a considerable period ot time, and this storage results in the thickening of the material due to decreasing moisture contents. Moisture content may range from about 99.5% to as low as 60%, but commonly is in the range from about 92% to 85% after several years of aging in the lagoon. As described in U.S. Pat. No. 3,796,658, at this common moisture level the sludge does not behave as a fluid, but rather, resembles a heavy viscous or soft gelatinous material having thixotropic tendencies.
The problems which are connected in cleaning lagoons or catch basins of this type are aggravated by the fact that (depending upon the constituency of the waste products disposed therein) chemical reactions, microbic growth, local geologic characteristics including soil porosity and water table levels, and the particular design and contruction of the lagoon or catch basin to be cleaned result in extremely discontinuous deposits of materials to be removed. For example, depending on exposure, porosity, dwell time in the lagoon, the varying nature of the substances charged into the lagoon from year to year, and many other factors, the consistency and handleability of waste material to be removed from within any given lagoon, much less from one lagoon to the next, will vary markedly by depth and region.
The parent applications referenced above with regard to the present invention generally disclose novel catch basin cleaning systems wherein various means are provided for transferring material obtained from the catch basin to subsequent processing operations only in the event that the material is determined by various monitors to be of an optimal nature for introducing into the subsequent process phase. For example, a pumping means will transfer materials to an equalization means only if that material contains a preselected percentage of solids, which percentage is selected for its compatability with the subsequent processing means which are mounted on an adjacent mobile apparatus. Additional means are provided to insure that a maximum flow of material will be produced. For example, ejectors are used in combination with novel optimal pumping, monitoring and recirculation means in order to insure that the liquid which is collected from the catch basin has neither too little or too great a solids content for subsequent equalization and dewatering operations. In the event that a liquid is being pumped by the pumping means which contains the optimum solids content, this liquid is admitted to a subsequent equalization process which equalizes, mixes and homogenizes the collected material for subsequent treatment. Dewatering, treatment, conditioning and discharge follow equalization and interact to produce the desired end products which often may be a cake material suitable for use as land fill material. Water suitable for return to the process head or sanitary sewer may be produced. Alternatively, water may be recirculated to be added directly into either the ejector system or to dilute the material which is being collected by the pumping system.
Throughout these processes, material which is collected from the catch basin, hereafter referred to as the wash effluent or wash stream, is monitored qualitatively and quantitatively at numerous stages of the processes. By monitoring the nature and quantity of this flow, the level of the equalization means, the density of the dewatering means input, the centrate turbidity centrate flow rate and centrate pH, various valves are automatically operated which regulate the bypass of the wash effluent back into the catch basin, the flow of material to the equalization means, the flow of thickened material either to the conditioning means or again to the equalization means, the flow of material to the process head or ejector, the amount of virgin water added to the pumping means, and the rates of the pumping means, dewatering means, treatment (chemical feed) means and conditioning means. As a result, these prior applications present systems capable of adapting superior dewatering equipment to the art of catch basin cleaning which, heretofore, has relied upon settling tank type processing in order to collect and then transport materials removed from catch basins.